Process and installation for separation of air by cryogenic distillation integrated with an associated process

ABSTRACT

In a process for separation of air by cryogenic distillation integrated with an associated process, air is separated in a separation unit ( 1 ), fluid is sent from the separation unit to an associated process, steam ( 3 ) is derived from the associated process, at least part of the steam is used in the separation unit and at least one fluid stream ( 11 ) is sent from the air separation unit to the atmosphere, at least when the steam is used in the air separation unit.

[0001] The present invention relates to a process and installation forseparation of air by cryogenic distillation, integrated with anassociated process.

[0002] Air separation units are frequently integrated with associatedprocesses producing large amounts of water vapour, such as gas-to-liquid(GTL) and gas-to-olefins (GTO) processes. On remote sites where thevapour cannot be used to generate energy and the vapour cannot beexported, the excess vapour, representing between 5 and 30% of the steamproduction, is generally sent to a condenser where it is converted intowater, as described in EP-A-0748763.

[0003] The air separation units generally supply oxygen enriched gas ata pressure exceeding 5 bar abs. to the associated process.

[0004] One object of the present invention is to reduce the size of thesteam condenser or even eliminate it completely, thereby reducing thecapital costs of the plant.

[0005] It is known from ‘The Future of Air Separation’, a conferencegiven by Dr. T. Rathbone at LTEC90, held in 1990, to couple a steamturbine using steam from a partial oxidation system with the compressorof an air separation unit.

[0006] EP-A-0562893 describes an air separation unit in which the aircompressor and nitrogen compressor are powered by a steam turbine.According to the present invention, there is provided a process forseparation of air by cryogenic distillation integrated with anassociated process comprising the steps of:

[0007] a) cooling compressed and purified air to a cryogenic temperaturein a heat exchanger by heat exchange with fluids separated in an airseparation unit

[0008] b) separating compressed, purified and cooled air in an airseparation unit to produce at least one fluid enriched in oxygen and/orat least one fluid enriched in nitrogen and possibly at least one fluidenriched in argon,

[0009] c) sending at least part of one said fluid to an associatedprocess,

[0010] d) deriving at least one stream of steam from the associatedprocess,

[0011] e)using at least part of the steam in the air separation unit,characterised in that it comprises operating the air separation unitwith at least one of the following process features:

[0012] i) operating the heat exchanger to have a temperature differencebetween a warm stream entering the heat exchanger and a stream leavingthe heat exchanger, having been warmed, of at least 5 K, preferably atleast 10 K, at its warm end and/or

[0013] ii) producing the fluid enriched in oxygen with a yield of lessthan 95%, preferably less than 90% and/or

[0014] iii) sending at least first and second fluid streams from the airseparation unit to the atmosphere and/or

[0015] iv) warming a fluid stream separated in the air separation unitagainst a stream of steam

[0016] wherein in the case where features i), ii) and/or iii) are used,and optionally in the case where feature iv) is used, at least one steamturbine is used to produce work and the work is used to supply at leastpart of the energy needs of at least one main compressor compressing airtreated in the air separation unit and/or an air booster compressing airwhich has already been compressed to a superatmospheric pressure and/ora compressor for gas enriched in oxygen or nitrogen.

[0017] In this way, the air separation unit functions in a way which isdeliberately chosen to be less than optimal for example by oversizingthe air separation unit, in order to use the steam in the air separationunit and avoid using a steam condenser or reduce the size of thecondenser, so as to reduce the overall costs for the whole of the siteincluding the air separation unit. Certainly energy is wasted byoperating the air separation unit in this way but the overall cost ofthe wastage is reduced.

[0018] In one embodiment of the invention, the process comprises sendingenergy to the atmosphere by sending at least first and second fluidstreams from the air separation unit to the atmosphere.

[0019] Preferably the first fluid stream sent to the atmosphere ispreviously used to regenerate the purification unit used to purify theair and the second fluid stream or streams sent to the atmosphere is airand/or is/are enriched in oxygen, nitrogen and/or argon and ispreferably at a pressure of at least 5 bar abs.

[0020] The second fluid stream or streams is/are preferably warmed toambient temperature in a heat exchanger and then sent directly to theatmosphere, possibly after an expansion step.

[0021] Alternatively or additionally, the second fluid stream or streamsis compressed air, removed before or after purification, preferably at apressure of at least 5 bar abs.

[0022] In a preferred embodiment, the column operating at the lowestpressure of the air separation unit (other than an argon column) isoperating at least 2 bar abs., preferably 4 bar abs.

[0023] Preferably, at least two air separation units supply fluid to theassociated process, each air separation unit being dimensioned toproduce N/N-1 multiplied by at least 80%, preferably 90% or even 100%,of the nominal flow, N being the number of air separation unitssupplying the associated process.

[0024] Preferably the process comprises expanding at least part of thevapour in at least one turbine coupled to at least one compressor of theair separation unit Preferably, at least one steam turbine is used toproduce work and the work is used to supply at least part of the energyneeds of at least one main compressor compressing air treated in the airseparation unit and/or an air booster compressing air which has alreadybeen compressed to a superatmospheric pressure and/or a compressor forgas enriched in oxygen or nitrogen.

[0025] For example, the at least one turbine may be coupled to a maincompressor compressing air treated in the air separation unit and/or toan air booster compressing air which has already been compressed to asuperatmospheric pressure and/or to a compressor for gas enriched inoxygen or nitrogen.

[0026] Alternatively the steam turbine may be used to generateelectricity and that electricity may be used to power at least one ofthe compressors of the air separation unit.

[0027] According to another embodiment of the process, the processcomprises sending energy to the atmosphere by sending refrigeration fromthe air separation unit to the atmosphere.

[0028] For example, vapour from the associated process may be sent to atleast one heat exchanger forming part of the air separation unit, atleast one cryogenic liquid produced in the air separation unit is sentto the at least one heat exchanger, at least one cryogenic liquidvaporises at least partially in the heat exchanger and is sent to theatmosphere and/or to an associated process in gaseous form.

[0029] Alternatively, vapour from the associated process is sent to atleast one heat exchanger of the air separation unit, at least onecryogenic fluid produced in the air separation unit is sent to the atleast one heat exchanger wherein it is warmed and the warmed cryogenicfluid is then expanded in a turbine before being sent to the atmosphere.

[0030] At least one fluid stream, other than that used for regeneration,is sent to the atmosphere from the air separation unit constantly orwhen the amount of steam derived from the associated process exceeds agiven value.

[0031] This fluid stream may represent at least 1% of the air separatedin the air separation unit, preferably at least 5%.

[0032] It may be an oxygen-enriched fluid, a nitrogen enriched fluid orair.

[0033] Preferably the fluid stream is warmed in the heat exchanger andthen sent directly to the atmosphere, without undergoing transformation.

[0034] In a particular embodiment, the fluid sent to the associatedprocess is an oxygen rich gas and the associated process is a partialoxidation process associated with a catalytic conversion processproducing excess steam.

[0035] Preferably the at least one fluid stream is not used or is onlypartly used to regenerate a unit used to remove humidity and carbondioxide from the feed air for the air separation unit or an airseparation unit and is not used or is only partly used in a waterchilling unit.

[0036] Preferably, steam is sent constantly or substantially constantlyto the air separation unit.

[0037] According to another embodiment of the invention, there isprovided an installation for separation of air by cryogenic distillationintegrated with an associated process including:

[0038] i) at least one air compressor for compressing air to be treatedin an air separation unit

[0039] ii) an air separation unit comprising a purification unit, heatexchangers, and at least one cryogenic distillation column

[0040] iii) means for supplying compressed air from the main aircompressor to the air separation unit

[0041] iv) means for removing a fluid enriched in a component of airfrom the air separation unit and sending it to an associated process

[0042] v) means for transferring steam from the associated process tothe air separation unit and

[0043] vi) means for sending at least one fluid stream from the airseparation unit to the atmosphere, without previously sending the fluidstream to regenerate an air purification unit.

[0044] The means for sending at least one fluid stream from the airseparation unit to the atmosphere may be connected to the main aircompressor and/or to a column of the air separation unit.

[0045] Preferably the installation comprises a steam turbine coupled tothe main air compressor and/or an air booster of the air separation unitand/or a gaseous product compressor of the air separation unit and meansfor feeding at least part of the steam from the associated process tothe steam turbine.

[0046] According to a further embodiment, the invention comprises aninstallation for separation of air by cryogenic distillation integratedwith an associated process including

[0047] i) at least one air compressor for compressing air to be treatedin an air separation unit

[0048] ii) an air separation unit comprising a purification unit, heatexchangers, and at least one cryogenic distillation column

[0049] iii) means for supplying compressed air from the main aircompressor to the air separation unit

[0050] iv) means for removing a fluid enriched in a component of airfrom the air separation unit and sending it to an associated process

[0051] v) means for transferring steam from the associated process tothe air separation unit,

[0052] vi) a heat exchanger,

[0053] vii) means for sending at least part of the steam from theassociated process to the heat exchanger and

[0054] viii) means for sending a cryogenic fluid from a column of theair separation unit to the heat exchanger to be warmed by indirect heatexchange with the steam, said heat exchanger being connected to themeans for sending at least one fluid stream from the air separation unitto the atmosphere and/or to the associated process. In one embodiment,the installation comprises means for expanding the fluid streamdownstream of the heat exchanger, for example a turbine.

[0055] Preferably the cryogenic fluid is a liquid, supplied from the airseparation unit and, possibly, from at least one other air separationunit and the cryogenic liquid is stored in a tank before being sent tothe heat exchanger. The tank (and possibly the pump, if the liquid ispressurised) may be common to the air separation unit and another airseparation unit or to all the air separation units.

[0056] Thus the air separation unit is voluntarily operated so as towaste energy, either in the form of one of the product gases or acompressed air stream by sending it to the atmosphere or in the form ofrefrigeration. This in fact proves to be more economical for the overallcost of the plant than the present techniques for disposing of theexcess steam, which are costly in terms of equipment and maintenance.

[0057] An oxygen enriched stream contains at least 30 mol. % oxygen,preferably at least 60 mol. % oxygen and still more preferably at least80 mol. % oxygen.

[0058] An argon enriched stream contains at least 30 mol. % argon,preferably at least 60 mol. % argon and still more preferably at least80 mol. % argon.

[0059] A nitrogen enriched stream contains at least 85 mol. % nitrogen,preferably at least 90 mol. % nitrogen and still more preferably atleast 95 mol. % nitrogen.

[0060] The air stream released to the atmosphere is at a pressure of atleast 5 bar abs. preferably at least 10 bar abs. or at least 20 bar absor at least 30 bar abs.

[0061] The oxygen enriched stream and/or nitrogen enriched streamreleased to the atmosphere is/are at a pressure of at least 10 bar abs.or preferably at least 20 bar abs or at least 30 bar abs.

[0062] It will be understood that the term ‘air separation unit’ mayinclude the main air compressors(s), booster compressor(s), productcompressor(s), product storage tanks or buffer tanks, heat exchangers,distillation columns, pump(s) and turbine(s). The term thus may coverelements within and without the cold box.

[0063] An air separation unit may include a single column, a doublecolumn (for example as described in FR-A-2477276, EP-A-0504029,FR-A-2688052 or EP-A0583189) or a triple column( for example asdescribed in EP-A-0538118) and possibly additionally at least one argonenrichment column and/or a mixing column (for example as described inEP-A-0531182).

[0064] The associated process may be any process consuming a fluidproduced by the air separation unit, such as an oxygen enriched streamand/or an argon enriched stream and/or a nitrogen enriched stream and/orcompressed air and which produces steam either directly from the stageof the process consuming the enriched stream or another stage of theprocess upstream or downstream that stage.

[0065] The term “treated in the air separation unit” covers separationby cryogenic distillation within the unit but also covers the case wherea stream is simply compressed by the main air compressor of the unit orby another process upstream of the columns.

[0066] The ‘nominal’ flow of the air separation unit is the maximum realproduct flow to the customer for which it is designed.

[0067] It will of course be understood that the gaseous stream may besent to the atmosphere either by sending them into the air, for exampleusing a device such as claimed in French Patent Application 2000-13382,or by sending them into a tank of water or a bed of solid material.

[0068] The invention will now be described in further detail withreference to the figures:

[0069]FIG. 1 is a schematic drawing of an air separation unit and a GTLprocess integrated to function according to the process of theinvention, with at least one compressor of the air separation unit beingcoupled to a steam turbine.

[0070]FIG. 2 is a schematic drawing of an air separation unit and a GTLprocess integrated to function according to the process of theinvention, with a heat exchanger in which steam is used to vaporise acryogenic liquid of the air separation unit.

[0071]FIG. 3 is a schematic drawing of an air separation unit and a GTLprocess integrated to function according to the process of theinvention, with a heat exchanger in which steam is used to warm acryogenic fluid of the air separation unit, before the fluid is expandedin a turbine.

[0072] In FIG. 1, natural gas is sent to a partial oxidation processusing oxygen from an air separation unit 1 to produce a synthesis gascontaining carbon monoxide and hydrogen. The synthesis gas is reactedcatalytically to produce higher molecular weight hydrocarbon productsand excess steam 3.

[0073] The air separation unit may be of any known type and may comprisea classical double column or a triple column. The air to be treated isfirst compressed in at least one main air compressor 5, which is coupledto a steam turbine 7 in which the excess steam 3 is expanded. The mainair compressor or compressors preferably compress the feed air tobetween 5 and 35 bar abs. Part of the air may then be compressed in abooster compressor 9, which is also coupled to the or a steam turbine.The Figure shows the compressor 9 as a cold booster but it may of coursehave an inlet temperature equal to or higher than the ambienttemperature.

[0074] The air is sent to the air separation unit wherein it isseparated to form at least a waste nitrogen stream 37 containing atleast 90 mol. % nitrogen, a nitrogen enriched gaseous product stream 27containing between 90 and 99.99 mol. % nitrogen (optional), a productargon stream 31 containing between 90 and 99,99 mol. % argon (optional),an oxygen enriched liquid stream 43 (optional), a nitrogen enrichedliquid stream 45 (optional) and an oxygen enriched gaseous stream 23containing between 70 and 99,8 mol. % oxygen with a yield of less than95%, preferably less than 90%. Preferably the nitrogen and argon streamseach contain less than 1 ppm oxygen. The waste nitrogen stream 37 onlyis used to regenerate the purification unit 35 of the air separationprocess. The heat exchanger 21 used to cool the air to a cryogenictemperature against product streams 23,27,31 is operated to have atemperature difference of at least 5 K, preferably 10K between thetemperature of the entering air and at least one of the product streamscoming from the warm end.

[0075] The product nitrogen and oxygen streams in gaseous form may beremoved from the column system in gaseous form or may be removed inliquid form from the column system and optionally pressurised in a pump(not shown).

[0076] It will be appreciated that, given the demands of the partialoxidation process, there are commonly several air separation units usedto provide the oxygen requirements and connected in parallel, forexample four air separation units, each having their own main aircompressor or compressors.

[0077] There may be a common air network for the compressed air linkingthe compressors of several air separation units. Similarly, there may bean oxygen network linking the oxygen outputs of several air separationunits.

[0078] If the amount of air compressed in the main air compressor orcompressors is such that the amount of oxygen produced would be surplusto the requirements of the partial oxidation process, various solutionsare possible according to the invention.

[0079] Firstly, the excess compressed air can be sent to the atmospherein a stream 11 upstream of the purification unit 35 and/or a stream 11Adownstream the purification unit and/or a stream 11B removed followingfurther compression in booster 9. In all cases the pressure of the air11,11A,11B exceeds 5 bar abs. and may exceed 15 bar abs.

[0080] In this case the columns of the air separation unit aredimensioned to produce the maximum amount of oxygen required by thepartial oxidation process and no streams are sent to the atmosphereexcept the air stream or streams 11,11A,11B and the stream 37 used forthe regeneration.

[0081] Alternatively or additionally, the columns of the air separationunit can be dimensioned to receive the excess compressed air and astream enriched in oxygen 25, nitrogen 29 or argon 33 can be released tothe atmosphere, since the amount of products produced exceeds therequirements of the partial oxidation process.

[0082] It will of course readily be seen that the excess air can bereleased to the atmosphere following distillation in the form ofdifferent streams having different compositions. Air may additionally besent to the atmosphere in the form of streams 11,11A,11B.

[0083] In the case of the figure, the streams form part of the normalproduct streams but it will readily be seen that the streams sent to theatmosphere may have a purity greater than or less than the productstream purity. For example, in the case where excess steam is available,a stream of oxygen enriched gas less pure than stream 23 may be sent tothe atmosphere.

[0084] Should the partial oxidation process require additional oxygen,the oxygen can be supplied by no longer rejecting the oxygen stream 25to the atmosphere or by reducing the oxygen enriched stream 25.

[0085] During start-up, the steam turbine 7 is driven by steam producedby a boiler fuelled by natural gas.

[0086] A or the steam turbine may additionally or alternatively becoupled to a compressor 13 for the oxygen enriched gas 23 or acompressor 15 for the nitrogen enriched gas 27, as shown in dashedlines.

[0087] In FIG. 2, natural gas is sent to a partial oxidation processusing oxygen from an air separation unit 101 to produce a synthesis gascontaining carbon monoxide and hydrogen. The synthesis gas is reactedcatalytically to produce higher molecular weight hydrocarbon productsand excess steam 103.

[0088] The air separation unit may be of any known type and may comprisea classical double column or a triple column as described in the patentsmentioned above. The air to be treated is first compressed in a main aircompressor, which may or may not be coupled to a steam turbine in whichpart of the excess steam is expanded, as in FIG. 1. Alternatively in thecase of FIG. 2, there need be no steam expansion step. The main aircompressor preferably compresses the feed air to between 5 and 35 barabs. Part of the air may then be compressed in a booster compressorbetween 10 and 70 bar abs., which could also be coupled to the steamturbine.

[0089] The air separation unit produces at least a gaseous oxygenenriched stream 123 and a liquid oxygen enriched stream 143.

[0090] When excess steam is available from the conversion process, astream 103 comprising all or part of the excess steam is sent to a heatexchanger 17 outside or inside the cold box where it exchanges heat witha stream of oxygen enriched liquid 143 and/or nitrogen enriched liquidand/or argon enriched liquid, so as to vaporise at least partially theliquid and form a gaseous stream, at least part 125 of which may bereleased to the atmosphere.

[0091] The liquid may previously have been stored in a storage tank 155and/or pressurised in a pump 151 inside or outside the air separationunit 101 before vaporisation. Additionally or alternatively liquid 153of the same of similar composition may be supplied from another airseparation unit or from a storage tank common to several of the airseparation units or all the air separation units or from a tanker truck.

[0092] In FIG. 2, the steam is used to vaporise only a stream containingbetween 60 and 99,8 mol. % oxygen 143 and the gaseous stream 125 formedis released to the atmosphere.

[0093] Should the partial oxidation process require additional oxygen,the oxygen can be supplied by no longer rejecting the oxygen enrichedstream 125 to the atmosphere or by reducing the oxygen enriched streamreleased to the atmosphere, as shown in dashed lines on the figure.

[0094] If the excess vapour is no longer available, the liquid stream isno longer sent from the air separation unit to the exchanger and the airseparation unit produces the liquid stream 143 as a final product.Obviously if the amount of excess vapour is simply reduced, a smalleramount of cryogenic liquid 143 may be sent from the air separation unitto the heat exchanger and the rest of the liquid constitutes a smallproduction of liquid.

[0095] Alternatively all the gas vaporised in the heat exchanger 17 maybe sent to the associated process. In this case it is not the gaseousproduct which is wasted but refrigeration, since it is a source ofirreversibility to produce the product in liquid form only to vaporiseit subsequently to form a gaseous product. In this case, the loss ofenergy is in the form of refrigeration, which may be sent to theatmosphere or transferred to the vapour stream.

[0096] A further object of the invention is a process for separation ofair by cryogenic distillation comprising the steps of

[0097] separating compressed and purified air in an air separation unitto produce at least one fluid enriched in oxygen and at least one fluidenriched in nitrogen and possibly at least one fluid enriched in argon,

[0098] characterised in that it comprises sending a gas streamcontaining at least 35 mol. % oxygen and/or at least 5 mol. % argon tothe atmosphere.

[0099] Preferably the stream sent to the atmosphere includes at least 60mol. % oxygen, or even at least 80 mol. % oxygen.

[0100] Preferably the stream sent to the atmosphere is not used or isonly partly used to regenerate the purification system of the airseparation unit.

[0101] In the case where one of the air separation units is not inoperation, it becomes possible to supply all the oxygen required, byvaporising stored liquid oxygen in the heat exchanger 17 of FIG. 2,which of course can be used even if the column system is not operating.

[0102] In the system of FIG. 3, a fluid stream 243 in liquid or gaseousform is removed from the air separation unit 201 and sent to heatexchanger 117 where it vaporises in the case of a liquid or is warmed inthe case of gas by indirect heat exchange with the stream of excesssteam 203. The gaseous stream produced 225 is expanded in a turbine 230and is sent to the atmosphere and/or to the associated process.

[0103] Whilst the processes of the Figures all use integration of theair separation unit with a GTL process, it will be readily apparent thatthis kind of integration may be used with any process, fed by the airseparation unit with compressed air or a fluid separated in the airseparation unit, from which steam may be derived such as a gas turbine.

1. Process for separation of air by cryogenic distillation integratedwith an associated process comprising the steps of a) cooling compressedand purified air to a cryogenic temperature in a heat exchanger (21) byheat exchange with fluids separated in an air separation unit b)separating compressed, purified and cooled air in an air separation unit(1,101) to produce at least one fluid enriched in oxygen (23,43,123)and/or at least one fluid enriched in nitrogen (27,45)and possibly atleast one fluid enriched in argon (31), c) sending at least part of onesaid fluid (23,43,123) to an associated process, d) deriving at leastone stream of steam (3,103) from the associated process, e) using atleast part of the steam in the air separation unit, characterised inthat it comprises operating the air separation unit with at least one ofthe following process features: i) operating the heat exchanger to havea temperature difference between a warm stream entering the heatexchanger and a stream leaving the heat exchanger, having been warmed,of at least 5 K, preferably at least 10 K, at its warm end and/or ii)producing the fluid enriched in oxygen with a yield of less than 95%,preferably less than 90% and/or iii)sending at least first and secondfluid streams (11,11A,11B,25,29,33,37) from the air separation unit tothe atmosphere and/or iv) warming a fluid stream separated in the airseparation unit against a stream of steam wherein in the case wherefeatures i), ii) and/or iii) are used, and optionally in the case wherefeature iv) is used, at least one steam turbine (7) is used to producework and the work is used to supply at least part of the energy needs ofat least one main compressor (5) compressing air treated in the airseparation unit and/or an air booster (9) compressing air which hasalready been compressed to a superatmospheric pressure and/or acompressor (13,15) for gas enriched in oxygen or nitrogen.
 2. Processaccording to claim 1 comprising sending at least first and second fluidstreams (11,11A,11B,25,29,33,37) from the air separation unit to theatmosphere wherein the first fluid stream (37)sent to the atmosphere ispreviously used to regenerate the purification unit used to purify theair and the second fluid stream or streams (25,29,33) sent to theatmosphere is/are enriched in oxygen, nitrogen and/or argon and ispreferably at a pressure of at least 5 bar abs.
 3. Process according toclaim 1 or 2 comprising sending at least first and second fluid streams(11,11A,11B,25,29,33,37) from the air separation unit to the atmospherewherein the second fluid stream or streams (11, 11A, 11B) is compressedair, removed before or after purification, preferably at a pressure ofat least 5 bar abs.
 4. Process according to any preceding claim whereinat least two air separation units (1,101) supply fluid to the associatedprocess, each air separation unit being dimensioned to produce N/N-1multiplied by at least 80%, preferably 90% or even 100%, of the nominalflow, N being the number of air separation units supplying theassociated process.
 5. Process according to any preceding claimcomprising expanding at least part of the vapour (3,103) in at least oneturbine (7) coupled to at least one compressor (5,9,13,15) of the airseparation unit.
 6. Process according to any preceding claim wherein atleast one steam turbine (7) is coupled to at least one main compressor(5) compressing air treated in the air separation unit and/or to an airbooster (9) compressing air which has already been compressed to asuperatmospheric pressure and/or to a compressor (13,15) for gasenriched in oxygen or nitrogen.
 7. Process according to any precedingclaim comprising warming a fluid stream separated in the air separationunit against a stream of steam wherein vapour (103) from the associatedprocess is sent to at least one heat exchanger (17) forming part of theair separation unit, at least one cryogenic liquid (143) produced in theair separation unit is sent to the at least one heat exchanger, the atleast one cryogenic liquid vaporises at least partially in the heatexchanger and is sent to the atmosphere and/or to an associated processin gaseous form (125).
 8. Process according to any preceding claimcomprising warming a fluid stream separated in the air separation unitagainst a stream of steam wherein vapour (203) from the associatedprocess is sent to at least one heat exchanger (117) of the airseparation unit (201), at least one cryogenic fluid produced in the airseparation unit is sent to the at least one heat exchanger wherein it iswarmed and the warmed cryogenic fluid is then expanded in a turbine(227) before being sent to the atmosphere.
 9. Process according to anyof claims 1 to 8 wherein at least one fluid stream(11,11A,11B,25,29,33,125), preferably an oxygen enriched gaseous stream,is sent to the atmosphere from the air separation unit constantly orwherein at least one second fluid stream (11,11A,11B,25,29,33,125) issent to the atmosphere from the air separation unit substantiallyconstantly.
 10. Process according to any of claims 1 to 8 wherein atleast one fluid stream (11,11A,11B,25,29,33,125), preferably an oxygenenriched gaseous stream, is sent to the atmosphere from the airseparation unit when the amount of steam derived from the associatedprocess exceeds a given value or wherein at least one second fluidstream (11,11A,11B,25,29,33,125) is sent to the atmosphere from the airseparation unit when the amount of steam derived from the associatedprocess exceeds a given value.
 11. Process according to any precedingclaim wherein the fluid sent to the associated process is an oxygen richgas (23, 123) and the associated process is a partial oxidation processassociated with a catalytic conversion process producing excess steam.12. Process according to any preceding claim wherein the at least onefluid stream (11,11A,11B,25,29,33,125) is not used or is only partlyused to regenerate a unit (35) used to remove humidity and carbondioxide from the feed air for the air separation unit or another airseparation unit and is not used or is only partly used in a waterchilling unit.
 13. Process according to any preceding claim wherein afluid sent from the air separation unit to the associated process and afluid sent from the air separation unit to the atmosphere have the sameprincipal component, the fluid sent to the associated process being lesspure or purer than the fluid sent to the atmosphere.
 14. Processaccording to any preceding claim wherein steam is sent constantly orsubstantially constantly to the air separation unit (1,101,201). 15.Installation for separation of air by cryogenic distillation integratedwith an associated process including: i) at least one air compressor (5)for compressing air to be treated in an air separation unit ii) an airseparation unit comprising a purification unit (35), at least one heatexchanger (21), and at least one cryogenic distillation column (41) iii)means for supplying compressed air from the main air compressor to theair separation unit iv) means for removing a fluid enriched in acomponent of air from the air separation unit and sending it to anassociated process v) means for transferring steam (3) from theassociated process to the air separation unit and vi) means for sendingat least one fluid stream (11,11A,11B,25,29,33,125) from the airseparation unit to the atmosphere, without previously sending the fluidstream to regenerate the air purification unit.
 16. Installationaccording to claim 15 wherein the means for sending at least one fluidstream (11,11A,11B) from the air separation unit to the atmosphere isconnected to the main air compressor (5).
 17. Installation according toclaim 15 or 16 wherein the means for sending at least one fluid stream(25,29,33,125) from the air separation unit to the atmosphere isconnected to a column of the air separation unit.
 18. Installationaccording to any of claims 15 to 17 comprising at least one steamturbine (7) producing work and means to use the work for the energyneeds of the main air compressor (5) and/or an air booster (9) of theair separation unit and/or a gaseous product compressor (13,15) of theair separation unit and means for feeding at least part of the steam (3)from the associated process to the steam turbine(s).
 19. Installationfor separation of air by cryogenic distillation integrated with anassociated process including: i) at least one air compressor (5) forcompressing air to be treated in an air separation unit ii) an airseparation unit comprising a purification unit, at least one heatexchanger (17,117), and at least one cryogenic distillation column iii)means for supplying compressed air from the main air compressor to theair separation unit iv) means for removing a fluid enriched in acomponent of air from the air separation unit and sending it to anassociated process v) means for transferring steam from the associatedprocess to the air separation unit, vi) means for sending at least partof the steam (103) from the associated process to the heat exchanger andvii) means for sending a cryogenic fluid (143) from a column of the airseparation unit to the heat exchanger to be warmed by indirect heatexchange with the steam, said heat exchanger being connected to themeans for sending at least one fluid stream from the air separation unitto the atmosphere and/or to the associated process.
 20. Installationaccording to claim 19 comprising means for expanding the fluid streamdownstream of the heat exchanger (117).
 21. Installation according toclaim 19 or 20 wherein the cryogenic fluid is a liquid, supplied fromthe air separation unit and, possibly, from at least one other airseparation unit and wherein the cryogenic liquid is stored in a tank(155) before being sent to the heat exchanger (17).